Radio transmitter amplifier



Patented Mar. 4, 1947 RADIO TRANSMITTER AMPLIFIER Donald L. Hings, Ottawa, Ontario, lanada, as-

signor to ElectronicLaboratories, Inc., Indian apolis, Ind}, a corporation of Indiana Application August 8, 1942, Serial No. 454,083

In Canada August 6, 1942 2 Claims.

My-invention relates in general to a radio amplifier for-supplying power to a load circuit and more specifically to a radio amplifier having an expansion control circuit arranged to increase the power suppliedto the load circuit during modulation. An object of my invention is the provision of a radio-amplifier arranged to be connected between a: load circuit and a terminal energized by a source of modulated radio frequency wherein the radio amplifier is arranged'to increase the power supplied to the load circuit during modulation.

Another object of my invention is the provision of a radio amplifier having an amplifying circuit and an expansion control circuit, wherein both circuits are connected to a source of modulated radio frequency.

'Another object of my invention is the provision: of connecting both the amplifying circuit and the expansion control circuit to the source otfmodulated. radio frequency through a tuned resonant circuit;

Another object of my invention is the provisi'on"ofsubstantially'matching the impedance of theamplifying circuit of my radio amplifier to theiimpedance. of the'sour'ce o-f modulated radio frequency. t

Another object of my invention is the provision ofmatching the impedance of the expansion control circuit as: well as the impedance of the amplifyingcircuit to theimpedance of the source ormodulated radio frequency.

:Another object of my invention is the provisiorr of connecting my radio amplifier to the source of modulated radio frequency through means of a common conductor haVing twobranch circuits, wherein the amplified circuit is connected to one of the branches and wherein the expansion control circuit isv connected to the other branch.

- Another object of my invention isthe provision of. connecting the two branches to the common conductor through a tuned resonant circuit.

. Another object of my invention is the provision of. a-.--radio amplifier which will automatically work either from a source of modulated radio frequency or froma source of unmodulated radio frequency; in the latter case the expansion control circuit remaining inactive.

Other objects and a fuller understanding of my invention may behadby referring to the following; description and claims, taken in conjunction with the accompanying drawings,- in which- A .li igure lshowsthegmanner. in which my radio 2 l amplifiermay be connected to a source of modu lated radio frequency, wherein the output of-the radio amplifier is arranged to energizethe ana tenna load circuit;

Figure 2 illustrates diagrammatically a, radio amplifier embodying the features of my'i'nvention;

Figure 3' is a wave representation of thecar rier and the modulated radio frequency'without the power expansion;

Figure 4 is a viewwhich is shown in comparison with Figure 3 illustrating the carrier" wave and the modulated radio frequency wave" with. ex-- panded power.

With reference to Figure 1 of the drawing, my radio amplifier is designated generally by'the reference character I I and is arranged'to have-its" input connected to a source of'modulated radio, frequency which is illustrated generally by the reference character I'D. The output of the radio amplifier II is arranged to supply energy to an antenna l2. There are many applications today where it is desirable to increase the power delivered to an antenna or other load circuit from the existing equipment. An illustrationr of existing equipment would be where the antenna l2 was directly connected by the antenna cable' [8' and the connecting plug 20 to the output terminal 13 of the source'of modulated radio frequency [0. With my invention. I disconnect the antenna from the output terminal l3 of the source of modulatedv radio frequency and connect the in put of my radio amplifier II to the outputiterminal I3 and then connect the antenna l2 to'the amplifier output terminal l9, so as to deliver in? creased power to the antenna; Asshown in Fig.- ure 1, the input terminal M of my radio amplifier ll may be connected to the output terminal l3 of the source of modulated radio frequency by a cable I! having a: connecting plug I5 o-n'the lefthand end thereof to fit into the output ter minal l3 and having a connecting plug l8 upon the righthand end thereof to fit into the input terminal [4. The cable I! maybe'shielded'so'that a common ground through the housings of both of the units maybe provided. In other words the shielding of the cable is arranged to keep the housings of the two units at acommonpo-tential, although other connections maybe provided for this purpose. In the event it becomes desirable to increase the power: delivered tothe antenna l2 from the source of modulated radio fre quency I0 -it is only necessary to insert myradio amplifier in: the circuit as-:shown.- in;Fig,ure

for deliveringythez increaseiamount .ofmower to constitute a triode.

ing tube 26 which is connected to the input terminal l4 through a tuned coupler illustrated generally by the reference character 21. The output circuit for the amplifier tube 25 is connected to the output terminal [9 through an output antenna coupler illustrated by the reference charactor 28.

The amplifier tube 26may be of any suitable type and I find from practice that a beam type tube works very satisfactorily. The beam form- 4 ing plates of the tube are illustrated by the ref- 7 erence character 32 and are connected to ground.

The cathode 29 of the tube is heated from a filament supply indicated generally by the reference character 31.- The control grid 39 is connected to thetuned coupler 21 and the plate 33 is connected to the output antenna coupler 28 through a blocking condenser 34. The screen grid 3| is bypassed to groundthrough a by-pass condenser 42, and is supplied with energy from a screen supply 43. Theplate voltage for the amplifier tube 26 is supplied, from a plate supply indicated enerally by thereference character 40 through a radio frequency choke 4|. The output antenna coupler 28 which couples the plate 33 to the output terminal l9 and the antenna {2 comprises a tuning inductance 35 and tuning condenser 36 which is connected to ground.

The control grid 30 of the amplifier tube 26 isbiased with respect to the cathode 29 from a bias supply indicated generally by the reference character '18 through a resistor 1'! and the coupler inductance 44 of the tuned coupler 21. The operation of the amplifier tube 26 is controlled by the control grid 30 for supplying amplified'power to theantenna [2. The tuned cou-' pler 21 which comprises the inductance 44 and the variable condenser 45 may be tuned to r'esonance so that, the maximum voltage may be applied to the grid 39. The inductance 44 is provided with avariable tap 48 which is connected to the commonco-nductor 41 that leads to the input terminal l4. Accordingly, with this arrangement the impedance of the source of modulated radio frequency [B may be matched by adjustably setting the tap 48.

- .The description up to the present time dealt with the radio frequency amplifiercircuit 24. I will next describe the arrangement of the expansion control circuit designated generally by the reference character 25 which comprises a rectifier-amplifier tube 50 and a bias control tube 5!.

I The rectifier-amplifier tube 5!) may be a "dual purpose tube in which the cathode 53 and the plate 54 constitute a diode and in which the cathode 53, the 'platel55 and the control grid 56 The cathode 53 may be heated by a heater filament 52 which is supplied with energy from a filament supply 14. The diode plate 54 is coupled to the adjustable tap 49 onthe coupler inductance through a condenser 51. The plate 54 and the cathode 53 operate as a rectifier or detector and function to establish a voltage across the load resistance 59 whic is "proportional to the voltage of the source of modulated radio frequency Ill. The radio frequency current is prevented from flowing in the diode load resistance 59 by means of a radio frequency choke 58. The voltage which appears across the diode load resistance 59 is proportionalto the modulation and is impressed upon the control grid 56 througha. coupling condenser 62. In this manner; the amplified output of the rectifier-amplifier tube is proportional to the modulation. The cathode 53 is maintained at a positive bias by means of a cathode resistance 6| which is by-passed to ground through a cathode by-pass condenser 60. The control grid 56 is connected to ground through a grid resistor 63. The amplified output of the rectifier-amplifier tube 59 is fed into the bias control tube 5| through a coupling transformer 64. The voltage of the triode plate 55 is supplied by the plate supply 19 through the primary winding of the transformer 64'. The bias control tube 5! comprises a cathode 69, two control grids l9 and 12, and two plates II and 13 connected in parallel to ground. The cathode 69 may beheated by a heater filament 68'supplied with energy from the filament supply 14. The control grids 10 and 1-2 are connected respectively to the two ends of the secondary winding of the coupling transformer 64. A bias battery 15 is connected to the center tap of the secondary winding so that the control grids l0 and 12 will be maintained at a sufficiently high bias to prevent any current from fiowing from the cathode 69 to ,the plates ll and'l 3 when no modulated energy is being received by the transformer 64 from the tube 50. When'amplified modulated energy is being received by the transformer 64 from the tube 50, the bias control tube 5| operates to pass current -from the bias supply 18 through the resistor 'l'L-thecathode B9 and the plates H and l3. The fiow of current through the resistor ll causes a voltage drop thereacross which in turn reduces the negative bias of the control grid 30 of the. amplifier tube 25. The reduction in the negativeqbias: of the control grid 30 causes the amplifier tube- 26 to deliver more power to the antenna I2 during modulation. The tube 5|. passes current for both the negative and positive peaks of the modulated waves, and this action when taken 'in combination with the condenser 16 produces an integrated eifect to give a smooth performancexrela tive to changing the bias on the'grid 30 of the amplifier tube 26 to cause the tube to deliver an increased amount of power to the antenna during modulation. Thus'with reference to Figure 4, the dotted line illustrates diagrammatically the smooth and integrated expansion of the carrier, as affected by the combined actionof the bias control tube 5| ,the resistor 11 and the integrating condenser 16. The expanded-carrier occurs only during modulation and enables more power to be supplied to theantenna l2 for this period of time, when power is mostly needed. Figure 3 illustrates the carrier wave' and the modulated wave when there is no power expansion, wherein the dotted line 8| represents the fact'that the carrier is not ex' 'aan'ded during tor 41 by two branch circuits respectively through the tuned coupler 21. With this arrangement it is only necessary to have a single cable innerconnecting the source of modulated radio frequency l0 and my radio amplifier ll. As before explained, the common ground connection for the source of modulated radio frequency and my radio amplifier Il may be taken care of by a shield on the cable l1. Therefore my invention makes possible a quick change over from a source of low power supply to the antenna to a source of high power supply resulting from an expanded carrier to the antenna, without any special connections and without breaking into the housing which encloses the source of modulated radio frequency. Furthermore my radio amplifier may be connected to any source of modulated radio frequency regardless of the impedance thereof since I am able to match the impedance through the adjustable taps 48 and 49 on the coupler inductance 44.

The amplifying tube 26 functions as an amplifier'for all types of energies supplied to it by the source l0, but in addition functions to give an expanded carrier during modulation, sothat an increased amount of amplified power may be delivered during modulation over that delivered during an unmodulated wave. That is to say, the amplifying 26 is rendered more sensitive during modulation with the result that mor power is delivered to the antenna, or other output load, for an equivalent signal input during an unmodulated wave. Although I have shown and described my invention with a certain degree of particularity, it is understood that changes may be made therein without departing from the spirit of the invention which are included in the scope of claims hereinafter set forth.

I claim as my invention: 7

1. The combination with a housing having a source of modulated radio frequency therein and a terminal extending through the housing for conducting the source of modulated radio frequency to the outside of the housing, and a radio frequency'wave emitting load circuit arranged to be connected to said terminal, of a radio amplifier comprising a radio frequency amplifier circuit having an input and an output, means for disconnecting said load circuit from said terminal 6' andconnecting same to said output, a feed line shielded from the emitting load circuit for connecting said input to said terminal, an expansion control circuit energized from said terminal and arranged to increase the powersupplied'by said radio frequency amplifier circuit during modulation, and a common ground circuit for the source of modulated radio frequency and for the radio amplifier.

2. The combination with a housing having a source of modulated radio frequency therein and a terminal extending through the housing for conducting the source of modulated radio frequency to the outside oi'the housing, and a radio frequency wave emitting load circuit arranged to be connected to said terminal, of a radio amplifier comprising a radio frequency amplifier circuit having an input and an output, means for disconnecting said load circuit from said terminal and connecting same to said output, a feed line shielded from the emitting load circuit for connecting said input to said terminal, an expansion control circuit energized from said terminal and arranged to increase the power supplied by said radio frequency amplifier circuit during modulation, said source of modulated radio frequency being grounded to said housing, and connection means for grounding the radio amplifier to said housing.

DONALD L. HINGS.

REFERENCES CITED The following references are of record in the file of this patent: 

